In the setup shown below, a clear image of a distant object is obtained on the screen. The focal length of the concave mirror is:

Select from the following salts which may be used to prepare hard water required for the experiment.

A. CaSO₄

B. Na₂SO₄

C. CaCl₂

D. K₂SO₄

E. NaHCO₃

F. MgCl₂

Four students A, B, C and D did their experiment of finding the focal length of convex lens by obtaining image of a distant object as follows:

• Student A used the window grill in the laboratory as the object and a white paper sheet held in hand as the screen.

• Student B used a distant tree in the shade and a white thick held in a stand as the screen.

• Student C used a well illuminated laboratory window grill as the object and a white paper sheet held in a stand as the screen.

• Student D used a well illuminated distant tree as the object and a white thick board held in a stand as the screen.

Which student has used the correct method for performing experiment out of the above setups?

In the experiment on refraction of light through a rectangular glass slab done by four students A, B, C and D, the following observations were made:

(a) The emergent ray moves towards the normal after second refraction through glass slab with i = e

(b) The emergent ray moves away from the normal after second refraction through glass slab ∠ i < ∠e

(c) For any angle of incidence, always ∠I ˃ ∠e, always.

(d) The emergent ray moves away from normal after second refraction through glass slab with ∠i = ∠e

The student who has made the correct observation is:

To trace the path of ray of light through the triangular glass prism, a student observes that the emergent ray has